Applied Macro- and Sonoanatomy of the Lumbar Paravertebral Space

The positioning of the lumbar plexus within the psoas muscle is somewhat controversial. Winnie, for example, described the plexus as lying between the psoas and quadratus lumborum muscles. From this description, “psoas compartment block” was termed for the lumbar plexus block. Other names for the same thing are “lumbar plexus block”, “lumbar paravertebral block”, “quadratus lumborum block” and “fascia iliaca block” to name a few. Most authors described the plexus and its nerve branches within the psoas muscle between its anterior and posterior masses. The ventral rami of the first three and the major part of the fourth lumbar spinal roots (L2, L3, and L4) form the lumbar plexus. A contribution from the 1st lumbar nerve (L1) is common. As soon as the ventral rami of these spinal nerve roots exit the intervertebral foramina, they become embedded in the psoas muscle, anterior to the transverse processes. At the L4 to L5 level, however, the lumbar plexus branches are still medial and close to the transverse processes. The distance of the lumbar plexus to the skin varies with body habitus and gender. Capdevila and his colleagues described the distances as varying from 57 to 93 mm in women and from 61 to 101 mm in men.

The macro-, microanatomy, and sonoanatomy (static) of the lumbar plexus, its nerve roots, and relationships to other structures are discussed in this chapter.

Keywords: Acute pain medicine, Fascia iliaca, Femoral nerve, Genitofemoral nerve, Iliohypogastirc nerve, Ilioinguinal nerve, Intervertebral foramina, Lumbar paravertebral block, Lumbar plexus, Lumbar plexus block, Lumbosacral trunk, Macroanatomy, Microanatomy, Obturator nerve, Psoas compartment block, Psoas muscle, Quadratus lumborum block, Quadratus lumborum muscle, Regional anesthesia, Sciatic nerve, Sonoanatomy, Spinal nerve roots, Transverse processes, Ventral rami.